Electronic postage meter systems have been developed as for example the systems disclosed in U.S. Pat. No. 3,978,457 for Microcomputerized Electronic Postage Meter Systems, in U.S. Pat. No. 3,938,095 for Computer Responsive Postage Meter and in European Patent Application, Application Number 80400603.9, filed May 5, 1980 for Electronic Postage Meter Having Improved Security and Fault Tolerance Features. Electronic postage meters have also been developed employing plural computing systems. Such a system is shown in U.S. patent application Ser. No. 089,413, filed Oct. 30, 1979, now U.S. Pat. No. 4,301,507, for Electronic Postage Meter Having Plural Computing Systems and assigned to Pitney Bowes Inc.
The accounting circuits of electronic postage meters include nonvolatile memory capability to store postage accounting information. This information includes, for example, the amount of postage remaining in the meter for subsequent printing or the total amount of postage printed by the meters. Other types of accounting or operating data may also be stored in the nonvolatile memory. The memory function in the electronic accounting circuits have replaced the function served in previous mechanical type postage meter by mechanical accounting registers. Postage meters with mechanical accounting registers are not subject to the many problems encountered by electronic postage meters. Conditions cannot normally occur in mechanical type postage meters that prevent the accounting for a printing cycle or which result in the loss of data stored in the registers. Moreover, in mechanical postage meters it is not necessary to electronically monitor the position of the mechanical components associated with printing postage. This, however, is not the case with electronic postage meters.
Conditions can occur in electronic postage meters where information stored in electronic accounting circuits can be permanently lost. Conditions such as a total line power failure of fluctuation in voltage conditions can cause the microprocessor associated with the meter to operate erratically and either cause a loss of data or the storage of spurious data in the nonvolatile memory. Moreover, excessive heat within the confines of the meter housing can damage the nonvolatile memory, especially during a memory WRITE cycle for NMOS type nonvolatile memories. The loss of data or the storage of spurious data may result in a loss of information representing the postage funds stored in the meter. Since data of this type changes with the printing of postage and is not stored elsewhere outside of the meter, there is no way to recover or reconstruct the lost information. In such a situation, a user may suffer a loss of postage funds.
To minimize the likehihood of a loss of information stored in the electronic accounting circuit, efforts have been expended to insure the high reliability of electronic postage meters. Some systems for protecting the critical information stored in the meter are disclosed in the abovenoted patents and applications. An additional arrangement to protect the postage meter accounting information is shown in U.S. Pat. No. 4,285,050 for Electronic Postage Meter Operating Voltage Variation Sensing System.